A headspace sampler heats a liquid sample or a solid sample stored in a container at a preset temperature for a preset period of time to vaporize components having relatively low boiling points, collects a predetermined amount of gas containing these components (sample gas) from the upper space (headspace) of the container, and introduces the sample gas into a gas analyzer, such as a gas chromatograph (for example, refer to Patent Literature 1). Such a headspace sampler is suitably used for, e.g., chromatograph analysis of flavor ingredients in food, volatile organic compounds in water or the like.
FIG. 8 shows an example of a configuration of a conventional headspace sampler. This device includes a sampling unit 100 and a control unit 200, and collects a predetermined amount of sample gas from a sample container 11 set in the sampling unit 100 and introduces into a column (not shown) provided at a chromatograph analyzer.
In the sampling unit 100, a channel switching valve 20 is a rotary 6-port 2-position valve that includes six ports, or ports a to f, and switches to a connection state indicated by solid lines in FIG. 8 (hereinafter, referred to as a “load state”) or a connection state indicated by broken lines (hereinafter, referred to as an “injection state”) under control by the control unit 200.
The port a of the channel switching valve 20 communicates with a needle 10 for collecting sample gas (hereinafter, a channel connecting the port a to the needle 10 is referred to as a “channel F1”). The port b communicates with a gas inlet 41 for introducing gas (pressure gas) for pressurizing the inside of the sample container 11 and a gas outlet 51 for discharging the sample gas, via a branching pipe T1 (hereinafter, a channel between the branching pipe T1 and the gas inlet 41 is referred to as a “channel F2”, and a channel between the branching pipe T1 and the gas outlet 51 is referred to as a “channel F3”). On the channel F2, a solenoid valve SV1 is provided. On the channel F3, a solenoid valve SV2 is provided. The port c communicates with the port f via a measuring pipe 30 having a prescribed volume. The port d communicates with a gas inlet 42 for introducing carrier gas (hereinafter, a channel connecting the port d to the gas inlet 42 is referred to as a “channel F4”). The port e communicates with an inlet end of a column and a split channel F6, via a branching pipe T2 (hereinafter, a channel from the port e to the column is referred to as a “channel F5”). The split channel F6 is for discharging a part of sample gas without delivery to the column. At the tip end of this channel, a gas outlet 52 for discharging the sample gas is provided.
The gas inlet 41 and the gas outlet 51 communicate with a pressure control device (“APC” in the diagram) 61. Through this pressure control device 61, the pressure of gas flowing through the gas inlet 41 and the gas outlet 51 is controlled. On the other hand, the gas inlet 42 and the gas outlet 52 are controlled by a flow rate control device (AFC) 62. By means of this flow rate control device 62, the flow rate of gas flowing through the gas inlet 42 and the gas outlet 52 is controlled.
Hereinafter, procedures during introduction of sample gas into the column by the sampling unit 100 are described.
(i) Pressurizing Process
First, the solenoid valves SV1 and SV2 are closed, and the channel switching valve 20 is set to be in the load state, and, in this state, the needle 10 penetrates the sample container 11 and the distal end is disposed in the upper space (headspace) of the sample container 11. The sample container 11 is then heated by heating means, not shown, to a predetermined temperature. Subsequently, the solenoid valve SV1 is opened to introduce pressure gas from the gas inlet 41. Thus, the pressure gas is introduced into the sample container 11 and the inside of the sample container 11 is pressurized.
(ii) Equilibration Process
Next, the solenoid valve SV1 is closed, and this standby state is maintained for a predetermined time (which is referred to as “waiting time”). Thus, over a path from the sample container 11 then through the channel F1→the port a→the port f→the measuring pipe 30→the port c→the port b to the branching pipe T1, a region of the channel F2 between the branching pipe T1 and the solenoid valve SV1, and a region of the channel F3 between the branching pipe T1 and the solenoid valve SV2, the pressure and temperature of the inner space are equilibrated.
(iii) Sample Gas Collection Process
Subsequently, when the solenoid valve SV2 is opened, gas (sample gas) containing sample components vaporized in the sample container 11 flows through the needle 10 into the channel F1, passes through the channel switching valve 20 and flows into the measuring pipe 30. At this time, a part of the gas flowing into the measuring pipe 30 passes through the channel switching valve 20, the branching pipe T1 and the channel F3 and is discharged from the gas outlet 51. During the foregoing process, the carrier gas passes in an order from the gas inlet 42 to the channel F4→the port d→the port e→the channel F5 and flows into the column.
(iv) Sample Gas Introduction Process
Next, after the channel switching valve 20 is switched to the injection state, the carrier gas supplied from the gas inlet 42 passes in an order of the channel F4→the port d→the port c→the measuring pipe 30→the port f→the port e→the channel F5 and flows into the column. Thus, the predetermined amount of sample gas held in the measuring pipe 30 is introduced into the column together with the flow of the carrier gas. Parts of the carrier gas and sample gas flowing from the port e of the channel switching valve 20 and reaching the branching pipe T2 flow into the split channel F6 at a predetermined split ratio and are discharged from the gas outlet 52.